Infections due to extended-spectrum beta-lactamase producing Escherichia coli and Klebsiella species (ESBL-EK) have increased markedly. Few therapies exist for these organisms and infections due to ESBL- EK are associated with adverse clinical and economic outcomes. Effective approaches to curbing emergence of ESBL-EK remain unclear. Although prior antibiotic use has often been identified as an important risk factor for ESBL-EK colonization or infection, interventions to reduce antibiotic use have met with only limited success. Person to person transmission has also been repeatedly identified as an important component of the continued emergence of ESBL-EK. However, the ability of infection control strategies to limit ESBL-EK transmission has been largely untested and remains controversial. Critical to the success of interventions designed to reduce the incidence of ESBL-EK is identification of patients colonized and/or infected with these organisms. Comprehensive identification of such patients is needed to permit the accurate application of infection control measures (e.g., contact precautions) designed to prevent transmission of ESBL-EK. Two promising but untested strategies for limiting ESBL transmission through enhanced detection are: 1) screening of clinical E. co//'and Klebsiella spp urine isolates for ESBL- EK: and 2) active surveillance for ESBL-EK fecal colonization. In addition to identifying the impact of each specific intervention, the relative effectiveness (and cost-effectiveness) of these components must be clarified to identify the most efficient approach. Elucidating the epidemiology of ESBL-EK will also help target infection control interventions more precisely. Finally, efforts to discover unidentified aspects of ESBL-EK transmission are needed to further refine and optimize the infection control interventions. The specific aims of this application are divided into two phases: Phase I. Aim 1: to calculate the prevalence of ESBL-EK in clinical urine cultures; Aim 2: to identify the impact of screening for ESBL-EK in clinical urine cultures on ESBL-EK prevalence; Aim 3: to characterize the cost-effectiveness of screening for ESBL-EK in clinical urine cultures. Phase II. Aim 4: to calculate the prevalence of ESBL-EK fecal colonization; Aim 5: to identify the impact of an active surveillance program on ESBL-EK prevalence; Aim 6: to characterize the cost effectiveness of an active surveillance program. The secondary aims of this application are: 1) to develop and validate a prediction rule for ESBL-EK colonization on admission; 2) to identify risk factors for new fecal colonization with ESBL-EK; and 3) to identify risk factors for ESBL-EK infection in patients colonized with ESBL-EK. [unreadable] [unreadable] [unreadable]